The present invention relates to a method and an apparatus for scarfing surface defects of metal material, more particularly to a method of and an apparatus for instantaneously initiating such scarfing process.
In the usual case of conditioning, that is, removing defects of such products of iron works as steel slabs, blooms and billets with a scarfing machine, cold steel is so pretreated that its defects (hereinafter called the scarfing points) are heated locally with heat supplied from the scarfing nozzle until the temperature of the scarfing points has risen to such a degree as to make it susceptible of scarfing initiation. However, the temperature of the pre-heating flames issued from the scarfing nozzle is so low, and the heat thereof is so little, that a long time is required to raise the temperature of the scarfing points to the level for scarfing; the heat has mostly been transmitted into the inside of such steel piece because of high heat conductivity. This means low efficiency in the conditioning of such steel, particularly when it has a great number of defects on the surface.
In order to raise efficiency, effort has been exerted to shorten the time for scarfing initiation in the following ways:
1. Providing another nozzle for jetting metal powder in front of the scarfing nozzle, so that iron powder of 100 to 300 mesh is jetted into pre-heating flames. The vehement combustion heat energy produced by such iron powder combined with oxygen and the mechanical energy produced by the jets of iron powder heat, at a blow, the scarfing points locally, thereby making even cold steel susceptible of scarfing initiation in 4 or 5 seconds.
2. Sending forward a metal rod of small diameter (starting rod) until it contacts the scarfing points on the surface of to-be-scarfed metal material in front of the scarfing nozzle, and then heating the tip of said rod with the pre-heating flames issued from said scarfing nozzle, so that the tip of said rod melts continuously to produce droplets which heat or melt the surface defects of the material. Then scarfing oxygen is jetted from said scarfing nozzle toward the heated or molten scarfing points, to initiate the scarfing process.
However, such methods as mentioned above, have the following disadvantages: In the method (1), the nozzle for jetting metal powder may possibly have the jetting holes cloaked with spreading scarfing slag; the metal powder supplying device is difficult to operate; and it is impossible to initiate the scarfing process, while the to-be-scarfed metal material is travelling. Also, in the method (2), it takes 6 to 10 seconds before scarfing initiation, making impossible a flying start; such a long time required for scarfing intiation may cause excessively deep scarfing of the scarfing points, which should be avoided in the scarfing process.
For the scarfing of the side of a steel piece by any conventional scarfing method, it is necessary to turn up the side to be scarfed by an upper surface scarfing machine or provide another machine for scarfing the side of the steel pieces, making it necessary to also provide a reversing device in the former case or take a long time to scarf the side as well as the upper surface, hence much lower operation efficiency in the latter case.